A Global Positioning System (GPS) is a positioning system that may be used to determine the specific location of a GPS receiver by calculating ranges from the receiver to multiple satellites. Many mobile telephones include GPS functionality, which allow applications to identify the location of the mobile telephone and provide services based on that location, such as providing a map display or driving directions. GPS works well in environments that have a clear line of sight (LOS) between the receiver and transmitters (e.g., satellites) used to determine position of the receiver. However, GPS is not available or does not function well in all environments.
In indoor locations and other GPS-denied environments, other positioning systems may be used. One example is the GEOCOM Mobile Positioning System developed by The Boeing Company. The GEOCOM system combines local inertial, magnetic, and barometric data for each receiver with peer-to-peer ranging signals received from other receivers within a reception range. The peer-to-peer range estimates are combined with the local sensor data to determine accurate position estimates of each receiver.
But even with these positioning systems, signals may become corrupted by noise, interference, and multipath. Multipath occurs when signals do not directly travel to a receiver, but instead are reflected off of walls or other obstructions before arriving at the receiver. Thus, it is beneficial to develop ranging solutions that distinguish these reflected paths and account for their contributed errors. This is especially beneficial when the positioning system is being used in emergency situations where knowing the locations of users is critical.